Unbiased crop management advice

Monthly Archives: July 2018

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Staging canola for swathing or pre-harvest desiccation is critical to maintain high quality seed and maintain yield. Ideal swath timing is when 60% of seeds on the main stem have turned colour, meaning 60% of all the main stem seeds are showing some form of colour (yellow, brown, black) other than green.

For 60% seed colour change, the bottom third of the main stem of the plant will have totally brown/black to purplish seeds, the middle third will have turned, or be showing some spots of colour, and the top third are green. The green seeds must be firm and should roll between your fingers without squishing. At this stage, the average moisture content is about 30%.

Producers are reminded that more than one area in a field will need to be assessed for seed colour change. Relying on a visual assessment of canola pod colour alone will not provide an accurate estimate of crop stage. In many cases, the outside of the pod colour can turn brownish yellow but seeds inside may still be green.

Earlier swathing tends to lock in green chlorophyll in underdeveloped seeds, reducing oil content and potentially causing marketing issues. Canola can be swathed in the 30-40% seed colour change stage to manage a large number of acres ripening at the same time, but producers should be aware that swathing at this stage can cause yield losses up to 8%.

Dry growing conditions and damaging weather have impacted canola development across Manitoba in 2018. Evaluating canola fields for evenness and uniformity is important to selecting the right time to swath or desiccate the crop. If growth conditions allowed large patches of delayed emergence, or hail set back crop development, estimating the patch size and managing the crop according to the largest percentage area is a good recommended practice.

In general, a pre-harvest aid (glyphosate and Heat LQ) should be used to increase plant tissue drydown and kill green weeds. The correct stage is 60-75% seed colour change. Expect to harvest the crop 1-3 weeks after spraying, similar to the time expected between swathing and harvesting.

A desiccant with the active ingredient diquat works more quickly, forcing removal of crop moisture. A fast-acting product, expect to harvest 4-7 days after application. Target a minimum of 90% seed colour change, as diquat will lock in any remaining green chlorophyll in the seed.

Points to Consider

Caution is advised when swathing or desiccating a canola crop, since that is considered growth and development termination, according to pre-harvest interval (PHI) standards. Know the length in days PHI of the fungicide and/or insecticide used on the crop; swathing or desiccating should not take place before that PHI window closes.

Because of our experience with crops and weeds, it’s no surprise that the general public often turns to agronomists for plant identification and management advice. And it’s usually about this time of year – when Ontario puts out giant hogweed advisories and big white umbels are in bloom across Manitoba – that these calls start to pour in.

Cow Parsnip

Fortunately, it’s probably not giant hogweed (Heracleum mantegazzianum) since that invasive species has yet to be found in our province. It’s more likely another member of the carrot family – cow parsnip (Heracleum maximum). Unlike its giant cousin, cow parsnip is native to Manitoba and non-invasive. It’s also very attractive to pollinators.

But even though it’s probably not giant hogweed, it’s still best not to touch it. Because, much like its giant cousin, the sap of cow parsnip may cause dermatitis when in contact with exposed skin. Symptoms include photosensitivity, a rash and/or blisters. Reactions to cow parsnip sap are generally much less severe than those to giant hogweed sap.

Rust in sunflower is caused by the fungus Puccinia helianthi, which overwinters on plant stubble and produces five spore‐stages throughout the year. Early in the season, orange rust pustules appear on the upper surfaces of cotyledons of seedlings and volunteer plants, with later infections moving to the underside of the leaf (Figure 1). The most yield-damaging stage occurs in late July to early August, when symptoms of infection show up as dusty, dark brown pustules on leaf surfaces, petioles and flower bracts (Figure 2). As the disease develops, black teliospores form, overwintering on the crop residue.

Figure 1: rust on leaf underside (photo: MB Ag)

Figure 2: Rust on leaves, stem. Wilting plants (photo: MB Ag)

Sunflower rust becomes a more severe issue in later-planted crops, or crops with weaker genetic resistance. Warm, moist weather favours rapid multiplication of rust spores, and windblown spores can travel quickly from field to field. Early stages of sunflower rust in 2018 have been observed in the Cypress River area the week of July 3rd.

High plant populations and dense, leafy canopies allow humid conditions to remain in the crop throughout the day, compounding injury from rust spores.

Scout sunflower fields regularly to monitor the development and stage of rust infection. Watch for dense clusters of brown, powdery pustules scattered over all plant surfaces. Orange-brown ‘dust’ on clothing after being in a sunflower field is a key indicator that rust is present, and more careful scouting is needed. Withered lower leaves are an indication that the surface is heavily infected.

Controlling rust after infection is primarily done using triazole-based and strobilurin-based fungicides. Recommended action in rust-infected crops is to use a fungicide from the triazole group after the first onset of symptoms, at the 2-3% pustule coverage on the upper four leaves at flowering (R5). Strobilurin-based fungicides act more as a ‘protectant’, applied earlier before widespread infection occurs.

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Diseases: New clubroot cases have been confirmed in the Rural Municipalities of Lorne and Dufferin. Insects: Scouting for bertha armyworm continues with some reports of insecticide applications. Spider mites being noticed in some soybean fields. Grasshopper populations are variable. For full report see Insect & Disease Report – August 1, 2018

Crops are advancing rapidly with the warm and dry conditions. Rain is needed in most areas to sustain crops and replenish soil moisture. Harvested has started in winter cereals, barley, and peas. Swathing or pre-harvest applications have started in early seeded spring cereals and canola. Fist cut hay is nearing completion; yields are below normal. […]

Diseases: The second case of clubroot in canola this year has been reported. Disease surveys in soybean and wheat are ongoing and disease levels are low overall. Insects: Overall insect concerns in field crops are relatively low. There are still some areas where grasshopper levels are being watched. Spider mite levels are being monitored in some soybean fields in […]

Disease – Goss’s wilt was observed near St. Claude. Insects – Grasshopper populations are being monitored in and around the edges of some fields. Armyworms have been noticed in some cereal fields in the Central and Eastern regions. No soybean aphids have been reported yet. For more details and information see http://www.gov.mb.ca/agriculture/crops/seasonal-reports/manitoba-insect-and-disease-update-2018-07-11.html

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Favourable weather and field conditions have allowed seeding operations to begin, with a provincial estimate of <5% of the 2017 crop seeded. For the full crop report, see on-line at http://www.gov.mb.ca/agriculture/crops/seasonal-reports/crop-report-archive/crop-report-2017-05-01.html

The Guide to Crop Protection provides information on the use of herbicides, fungicides and insecticides for control of weeds, plant diseases and insects. This publication is only a guide. Always refer to the product label for application details and precautions. It is available: online at https://www.gov.mb.ca/agriculture/crops/guides-and-publications/#gfcp. Individual sections on Weed Control, Plant Disease Control and Insect […]

Did you know you can view the 2017 edition of Seed Manitoba, as well as past editions, on www.seedmb.ca? Well, you can! Flip-view digital editions of the current guide (2017), as well as the six most recent editions, are available at http://www.seedmb.ca/digital-edition/. Also, full PDF versions are available at http://www.seedmb.ca/digital-edition/pdf-editions-and-separate-section-pdfs/ where you can download the entire […]

http://www.gov.mb.ca/agriculture/crops/plant-diseases/clubroot-distribution-in-manitoba.html Map shows positive clubroot findings by Rural Municipality, discovered through laboratory testing for presence of clubroot spores in soil and/or positive confirmation of clubroot symptomatic plants. Testing was done from 2009-2014 and is still considered limited. Positive findings have been at low spore concentrations and sporadic throughout the province. As more fields are sampled, the map will be updated. As less than […]